1) Field of the Invention
The present invention relates to a method and apparatus for collecting low grade heat derived from solar energy and converting it into electricity without the use of any hydrocarbon fuels.
2) Related Art
The following definitions are used herein:
Solar Glass: A flat glass plate comprising one or two sheets of glass which transfers a high percentage of the solar energy striking it though both sides of the glass plate while reflecting only a small portion of the solar heat energy back into space for any given solar angle.
R-410a: Is a refrigerant liquid that exhibits a two-phase state, meaning it shifts from a liquid state to a gaseous state when heated. R-410a is used to carry out solar heat and the waste heat recovery because it conducts and stores heat well. R-410a also is used because it has no adverse impact on the environment.
Thermostatic Expansion Valve (TXV): A metering device the main purpose of which is to regulate the flow of a refrigerant, such as R-410a, into an evaporator (m, for example, a hybrid solar panel) at a rate that matches the amount of refrigerant being boiled off in the evaporator. It is actuated by changes in evaporator pressure and superheat of the refrigerant leaving the evaporator. Like all the other metering devices, it also provides a pressure drop in the system in which it is used, separating the high pressure side of the system from the low pressure side, thus allowing low pressure refrigerant to absorb heat onto itself.
Two Stage Air Motor: A motor in which the pressure of confined air causes the rotation of a rotor or the movement of a piston, to drive a second device connected to the rotor or piston. In addition, the air motor is designed with two sections i.e., a) one section optimized for operation using a refrigerant such as R-40I a, b) a second section optimized for operations using compressed nitrogen gas flow. Both sections are mechanically isolated from each other so there is no cross-contamination.
Piston Motor: A motor in which the pressure of an expanding gas causes the movement of a piston, which can be converted into rotating motion.
Thermal Conductivity: The heat flow across a surface per unit area per unit time, divided by the negative of the rate of change of temperature with distance in a direction perpendicular to the surface. Also known as the coefficient of conductivity when heat transfer takes place through conduction, convection and radiation.
High Pressure Line: A line or a pipe with pressure greater than 150 psi.
Low Pressure Liquid Line: A line or pipe with a pressure less than 150 psi.
Motor Generator Interface: The mechanical interface that connects any mechanical motor to an electrical generator for the purpose of generating electricity.
Motor Exhaust Port I: In a two-stage air motor, the exhaust port where a refrigerant, such as R-410a, is at lower dynamic pressure then at the inlet port.
Motor Exhaust Port II: In a two-stage air motor, the exhaust port from which Liquid Nitrogen (LN2) is expelled into the atmosphere.
Saturated Liquid: A liquid solution that contains enough of a dissolved solid, liquid, or gas so that no more will dissolve into the solution at a given temperature and pressure.
Geothermal Heat Sink: A heat sink that is designed to accept a saturated liquid of a given pressure and cool it to a point where it becomes a highly saturated liquid or completely liquid. In addition, it provides a second path for a different liquid like LN2 to extract heat from the surroundings area and convert the liquid into a high pressure gas at high flow rates using the stored heat energy found in the surrounding soil with which it is direct contact.
Circulation Pump: a specific type of pump used to circulate gases, liquids, or slurries in a closed circuit. They are commonly found circulating water in a hydraulic heating or cooling system. Because they only circulate liquid within a closed circuit, they only need to overcome the friction of a piping system (as opposed to lifting a fluid from a point of lower potential energy to a point of higher potential energy).
Generator Control Circuit: A simple control logic card that controls the output of the generator used to maintain voltage and current at some known state.
Solar Energy Density: The energy per unit volume of a region of space for a given location on the surface of the earth. Solar energy density is measured in watts per meter squared. Values vary with location and solar index. The average for Washington D.C. is about 1000 watts/meter-squared.
Hybrid Solar Collector Energy Density: The energy density for the location of a structure plus the potential energy from heat that has penetrated the roof of a structure and has accumulated inside its attic.
Latent Heat of Vaporization: The energy a substance absorbs from its surroundings in order to overcome the attractive forces between its molecules as it changes from a liquid to a gas at constant temperature and pressure, and in order to do work against the external atmosphere as it expands.
Waste Heat Collection: The collection of sensible heat in gases not subject to combustion and used for processes downstream in a system.
Evaporator: the part of a refrigeration system in which the refrigerant absorbs heat and changes from a liquid to a gas.
Liquid Nitrogen (LN2): Nitrogen that exists as a liquid at atmospheric pressure, at −195° C. (77.4 K).
Solar energy is abundant and an attractive method for collecting thermal energy. This area is only now being exploited. Solar photovoltaic devices dominate the collection of solar energy at this time and are used to convert solar energy directly into electricity but at a high cost and a low efficiency. The costs of solar photovoltaic panels are dropping in price, but are still out of reach for most people. Solar energy is collected using a large number of devices, concentrators, flat panels etc., but we still lack systems that are cost effective and can supply electricity in bad weather or at night for personal use. Large solar power plants have been constructed in California in the desert and have made some progress converting large amounts of solar energy into electricity. The down side is these large systems are not designed for the home owner.
Technology has advanced over the years regarding heating and air conditioning where these simple devices are found in almost every home. Modern day heating and cooling systems are being converted to the new R-410a refrigerant since it has less impact on the environment. These heating and cooling systems are only designed to produce heat or cold conditions, not convert or produce electricity. Geothermal heating and cooling systems have been used for years and only now are starting to gain acceptance. The primary use of geothermal energy is for heating and cooling, not for the production of electricity, except in special cases like in Iceland where hot springs are used to drive large steam turbines to produce electricity on a large scale. Thus, the current technology is distributed over a large area of applications.